Modelling of Coupled Shrinkage and Creep in Multiphase Formulations for Hardening Concrete.

The durability and serviceability of concrete structures is influenced by both the early-age behavior of concrete as well as its long-term response in terms of shrinkage and creep. Hygro-thermo-chemo-mechanical models, as they are used in the present publication, offer the possibility to consistently model the behavior of concrete from the first hours to several years. However, shortcomings of the formulation based on effective stress, which is usually employed in such multiphase models, were identified. As a remedy, two alternative formulations with a different coupling of shrinkage and creep are proposed in the present publication. Both assume viscous flow creep to be driven by total stress instead of effective stress, while viscoelastic creep is driven either by total or effective stress. Therefore, in contrast to the formulation based on effective stress, they predict a limit value for shrinkage as observed in long-term drying shrinkage tests. Shrinkage parameters for the new formulations are calibrated based on drying shrinkage data obtained from thin slices. The calibration process is straightforward for the new formulations since they decouple shrinkage and viscous flow creep. The different formulations are compared using results from shrinkage tests on sealed and unsealed cylindrical specimens. Shrinkage strain predictions are significantly improved by the new formulations.

Calibration of a Multiphase Model Based on a Comprehensive Data Set for a Normal Strength Concrete.

Hygro-thermo-chemo-mechanical modelling of time-dependent concrete behavior requires the accurate determination of a large set of parameters. In this paper, the parameters of a multiphase model are calibrated based on a comprehensive set of experiments for a particular concrete of grade C30/37. The experiments include a calorimetry test, tests for age-dependent mechanical properties, tests for determining the water desorption isotherm, shrinkage tests, and compressive creep tests. The latter two were performed on sealed and unsealed specimens with accompanying mass water content measurements. The multiphase model is based on an effective stress formulation. It features a porosity-dependent desorption isotherm, taking into account the time-dependency of the desorption properties. The multiphase model is shown to yield excellent results for the evolutions of the mechanical parameters. The evolution of the autogenous shrinkage strain and evolutions of the creep compliances for loading at concrete ages of 2 days, 7 days, and 28 days are well predicted together with the respective mass water content evolution. This also holds for the evolution of the drying shrinkage strain, at least for moderate drying up to one year. However, it will be demonstrated that for longer drying times further conceptual thoughts concerning the coupled representation of shrinkage and creep are required.

Long-Term Outcomes After Treatment With a Paclitaxel-Coated Balloon Versus Balloon Angioplasty: Insights From the PEPCAD-DES Study (Treatment of Drug-eluting Stent [DES] In-Stent Restenosis With SeQuent Please Paclitaxel-Coated Percutaneous Transluminal Coronary Angioplasty [PTCA] Catheter).

OBJECTIVES: The intention this PEPCAD-DES (Treatment of Drug-eluting Stent [DES] In-Stent Restenosis With SeQuent Please Paclitaxel Eluting Percutaneous Transluminal Coronary Angioplasty [PTCA] Catheter) study update was to demonstrate the safety and efficacy of paclitaxel-coated balloon (PCB) angioplasty in patients with DES-ISR at 3 years. BACKGROUND: In the PEPCAD-DES trial late lumen loss and the need for repeat target lesion revascularization (TLR) was significantly reduced with PCB angioplasty compared with plain old balloon angioplasty (POBA) in patients with drug-eluting stent in-stent restenosis (DES-ISR) at 6 months. We evaluated whether the clinical benefit of reduced TLR and major adverse cardiac events (MACE) was maintained up to 3 years. METHODS: A total of 110 patients with DES-ISR in native coronary arteries with reference diameters ranging from 2.5 mm to 3.5 mm and lesion lengths ≤22 mm were randomized to treatment with either PCB or POBA in a multicenter, randomized, single-blind clinical study. With a 2:1 randomization, 72 patients were randomized to the PCB group and 38 patients to the POBA group. At baseline, there were lesions with at least 2 stent layers in PCB (52.8%, 38 of 72) and POBA (55.3%, 21 of 38) patients. RESULTS: At 36 months, the TLR rates were significantly lower in the PCB group compared with the POBA control group (19.4% vs. 36.8%; p = 0.046). Multiple TLRs in individual patients were more frequent in the POBA group compared with the PCB group (more than 1 TLR: POBA, 13.2%; PCB, 1.4%; p = 0.021). The 36-month MACE rate was significantly reduced in the PCB group compared with the POBA group (20.8% vs. 52.6%, log-rank p = 0.001). CONCLUSIONS: PCB angioplasty was superior to POBA for the treatment of DES-ISR patients in terms of MACE and TLR for up to 36 months. There was no late catch-up phenomenon. (Treatment of Drug-eluting Stent [DES] In-Stent Restenosis With SeQuent® Please Paclitaxel Eluting Percutaneous Transluminal Coronary Angioplasty [PTCA] Catheter [PEPCAD-DES]; NCT00998439).

Arnold Durig (1872-1961): life and work. An Austrian pioneer in exercise and high altitude physiology.

Arnold Durig (1872-1961) grew up in the Austrian mountains in the period when intense exploration of the Alps started. As an enthusiastic mountaineer, scientist, and physician, he became one of the pioneers exploring physiological and pathophysiological aspects of humans sojourning to high altitudes. At the beginning of the 20(th) century, Durig was one of the great physiologists whose knowledge covered the whole field of physiology. Durig founded a renowned School and his students spread all over the world. He stayed in close contact with many colleagues and famous scientists, such as Albert Einstein and Sigmund Freud. Although he was an extremely productive and acknowledged physiologist and teacher at that time, his work and life are not very well known at the beginning of the 3(rd) millennium, even by high altitude physiologists. Thus, this article provides an overview on Durig's life and work, highlighting the most important scientific studies he performed at moderate and high altitudes, in an attempt to provide a few links to the development of high altitude research in the late 19(th) and early 20(th) centuries, complemented by some comments from a current point of view.

A randomized, multicenter, single-blinded trial comparing paclitaxel-coated balloon angioplasty with plain balloon angioplasty in drug-eluting stent restenosis: the PEPCAD-DES study.

OBJECTIVES: This study sought to define the impact of paclitaxel-coated balloon angioplasty for treatment of drug-eluting stent restenosis compared with uncoated balloon angioplasty alone. BACKGROUND: Drug-coated balloon angioplasty is associated with favorable results for treatment of bare-metal stent restenosis. METHODS: In this prospective, single-blind, multicenter, randomized trial, the authors randomly assigned 110 patients with drug-eluting stent restenoses located in a native coronary artery to paclitaxel-coated balloon angioplasty or uncoated balloon angioplasty. Dual antiplatelet therapy was prescribed for 6 months. Angiographic follow-up was scheduled at 6 months. The primary endpoint was late lumen loss. The secondary clinical endpoint was a composite of cardiac death, myocardial infarction attributed to the target vessel, or target lesion revascularization. RESULTS: There was no difference in patient baseline characteristics or procedural results. Angiographic follow-up rate was 91%. Treatment with paclitaxel-coated balloon was superior to balloon angioplasty alone with a late loss of 0.43 ± 0.61 mm versus 1.03 ± 0.77 mm (p < 0.001), respectively. Restenosis rate was significantly reduced from 58.1% to 17.2% (p < 0.001), and the composite clinical endpoint was significantly reduced from 50.0% to 16.7% (p < 0.001), respectively. CONCLUSIONS: Paclitaxel-coated balloon angioplasty is superior to balloon angioplasty alone for treatment of drug-eluting stent restenosis. (PEPCAD DES-Treatment of DES-In-Stent Restenosis With SeQuent® Please Paclitaxel Eluting PTCA Catheter [PEPCAD-DES]; NCT00998439).